Heat exchanger, method for producing a heat exchanger and power plant comprising such a heat exchanger

ABSTRACT

A heat exchanger and method for producing such a heat exchanger which during operation in a flow direction is flown through by a medium to be cooled and by two different cooling media. A power plant has a generator cooled by means of a generator cooling gas and a heat exchanger cooling the generator cooling gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2020/063124 filed 12 May 2020, and claims the benefit thereof.The International Application claims the benefit of German ApplicationNo. DE 10 2019 208 619.5 filed 13 Jun. 2019. All of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a heat exchanger through which a mediumto be cooled flows in a flow direction during operation thereof. Thepresent invention further relates to a process for producing such a heatexchanger. The invention additionally relates to a power plant having agenerator cooled by means of a generator cooling gas and a heatexchanger that cools the generator cooling gas.

BACKGROUND OF INVENTION

Power plants, for example gas turbine power plants, steam turbine powerplants, combined gas and steam turbine power plants, solar power plantsor the like, comprise a multitude of components that require cooling, inorder firstly to remove the waste heat that arises and secondly toincrease the output of the power plant. This is also true of thegenerator used for power generation, which is generally cooled withgenerator cooling gas recooled by means of a heat exchanger. The heatexchanger is usually connected to a closed cooling water system of thepower plant, via which further heat exchangers are also supplied withcooling water for example those for lubricant oil and/or sealing oilcooling, for cooling of pumps or the like. The cooling water of thecooling water circuit can be re-cooled in various ways, for example bymeans of fresh water flow cooling, circulation cooling using a coolingtower or air-cooled coolers, etc.

A possible achievable electrical power in the generator depends on thecold gas temperature of the generator cooling gas defined for cooling ofthe generator windings, i.e. the generator cooling gas temperature onentry into the generator. The lower the cold gas temperature, the moremechanical energy can be converted to electrical energy in thegenerator. The generator cooling gas is recooled as described abovewithin a heat exchanger, through which cooling water from the coolingsystem of the power plant flows. Thus, the cold gas temperature of thegenerator cooling gas is coupled to the cooling water temperature of thecooling water flowing through the heat exchanger. The cooling watertemperature in turn is dependent on the recooling of the cooling waterand consequently cannot be lowered at will. There are thus limits to theelectrical power achievable in the generator.

If power-increasing measures on the turbine of the power plant result ina rise in mechanical power at the generator shaft, it would be desirableto provide improved cooling for the generator in order to be able toconvert more power to electrical energy therewith.

SUMMARY OF INVENTION

Proceeding from this prior art, it is an object of the present inventionto provide improved cooling, especially improved generator cooling.

This object is achieved by the present invention by providing a heatexchanger comprising a first stack of fins having a multitude of firstfins stacked in a stacking direction that extends transverse to the flowdirection, wherein the first fins are each provided with a multitude offirst passage holes that are flush with one another in stackingdirection, at least one further stack of fins arranged adjacent to thefirst stack of fins in flow direction, and having a multitude of secondfins stacked in the stacking direction, wherein the second fins are eachprovided with a multitude of second passage holes that are flush withone another in stacking direction, first pipe conduits that extendthrough the first passage holes of the first fins of the first stack offins and are press-fitted with the first fins, second pipe conduits thatextend through the second passage holes of the second fins of the atleast one further stack of fins and are press-fitted with the secondfins, wherein the first pipe conduits and the second pipe conduits arenot connected to one another for flow purposes and are provided forpassage of a first cooling medium and a second cooling medium, whereinthe cooling media are different from one another, and at least one coverthat connects the first stack of fins and the at least one further stackof fins to one another, which is placed atop an outer first fin of thefirst stack of fins and atop the adjacent outer second fin of the atleast one further stack of fins and covers these fins, wherein the atleast one cover has been provided with first passage holes arranged andformed so as to correspond to the first passage holes of the first finsof the first stack of fins, through which the first pipe conduits areguided, and has been provided with second passage holes arranged andformed so as to correspond to the second passage holes of the secondfins of the at least one further stack of fins, through which the secondpipe conduits are guided.

Such a heat exchanger is advantageous in that it can be operated withtwo different cooling media. The first cooling medium may be coolingwater, for example. The second cooling medium used may, for example, bea coolant which is recooled in a cooling unit. If the medium to becooled is generator cooling gas, the cold gas temperature thereof onentry into the generator is not limited by the degree of recooling ofthe cooling water of the cooling water system of the power plant.Instead, the cold gas temperature of the generator cooling gas can belowered further via heat exchange with the coolant that flows throughthe heat exchanger, such that it can be adapted flexibly to the coolingdemand of the generator if, for example, power-increasing measures areundertaken on the turbine. A further advantage of the heat exchanger ofthe invention is that the mechanical coupling of the stacks of finsthrough which the different cooling media flow via the at least onecover imparts very good mechanical stiffness to both stacks of fins witha simultaneously very inexpensive construction of low volume, even ifone of the stacks of fins in itself should have only very low intrinsicstiffness, for example, on account of low construction depth. This isimportant especially when an existing heat exchanger in which thegenerator cooling gas has to date been recooled by means of coolingwater only is to be replaced by a heat exchanger of the invention inorder to lower the cold gas temperature of the generator cooling gas byadditional cooling by means of a coolant. In such cases, theconstruction space available is defined by the dimensions of the oldheat exchanger and is very limited. Correspondingly, barely any space isavailable for a stack of fins through which a second cooling mediumflows, and therefore this second stack of fins can frequently beexecuted only with a very low construction depth, which leads to lowintrinsic stiffness.

In one configuration of the heat exchanger of the invention, the firstfins have a greater area than the second fins. In other words, thedimensions of the fins of the respective stacks of fins are matched tothe respective cooling medium.

The design of the surface of the first fins is advantageously differentthan the design of the surface of the second fins. In this way too, itis possible to achieve adaptation of the stacks of fins to therespective cooling medium.

Advantageously, the first fins and the second fins have been producedfrom a sheet material, for example from aluminum, in order to achievegood thermal conductivity.

In one configuration of the heat exchanger of the invention, a distancebetween the first fins in stacking direction is different than thedistance between the second fins in stacking direction, advantageouslygreater.

According to the invention, the first fins and the second fins may havebeen produced from a sheet material having a coating on one or bothsides.

The first pipe conduits are each connected to one another via U-shapedconnecting conduits, and the first cooling medium flows through themsuccessively, and/or the second pipe conduits are each connected to oneanother by U-shaped connecting conduits, and the second cooling mediumflows through them successively.

The flow cross section of the first pipe conduits is advantageouslydifferent than the flow cross section of the second pipe conduits,advantageously greater.

In one configuration of the present invention, the first pipe conduitsand the second pipe conduits have been produced from a metallicmaterial, advantageously from copper, which achieves good thermalconductivity.

Advantageously, the inner faces of the first pipe conduits and/or theinner faces of the second pipe conduits are structured in order toincrease their size, which is conducive to better heat transfer.

An arrangement pattern of the first passage holes advantageously differsfrom the arrangement pattern of the second passage holes.

The at least one cover has advantageously been produced from a metallicmaterial, advantageously from a metal sheet. This leads to a simple andinexpensive construction of the at least one cover.

Advantageously, the at least one cover encompasses the first stack offins and the at least one further stack of fins on opposite sides, whichfurther increases the mechanical stiffness of the construction.

In one configuration of the present invention, the first stack of finsand the at least one further stack of fins are joined to one another viaat least one side section. Such a side section is also very conducive tothe mechanical stiffness of the construction.

The present invention further provides a process for producing a heatexchanger designed in accordance with the invention, in which the firstfins and the second fins are produced simultaneously in a single fincompression device, for example using a fin compression mold thatdefines both features of the first fins and features of the second fins.In this way, very effective manufacture of the heat exchanger of theinvention is achieved.

The first pipe conduits and the second pipe conduits are advantageouslyexpanded simultaneously in a pipe conduit expansion machine. Suchsimultaneous expansion is also very conducive to effective manufactureof the heat exchanger of the invention.

The present invention additionally provides a power plant having agenerator cooled by means of a generator cooling gas and a heatexchanger of the invention that cools the generator cooling gas.

Advantageously, the first cooling medium that flows through the heatexchanger is cooling water, and the second cooling medium that flowsthrough the heat exchanger is a coolant, for example tetrafluoromethane(R-134a) or carbon dioxide.

Further features and advantages of the present invention become clearfrom the description that follows with reference to the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show:

FIG. 1 a schematic view of a power plant in one embodiment of thepresent invention;

FIG. 2 a schematic view of one embodiment of a heat exchanger of theinvention in the power plant shown in FIG. 1;

FIG. 3 a schematic side view in the direction of the arrow III in FIG.2, showing a first stack of fins and a second stack of fins of the heatexchanger, omitting struts and an upper and lower cover for illustrationpurposes;

FIG. 4 a top view of a first fin of a first stack of fins of the heatexchanger shown in FIG. 2;

FIG. 5 a top view of a second fin of a further stack of fins of the heatexchanger shown in FIG. 2;

FIG. 6 a schematic view of a fin production machine for production ofthe fins shown in FIGS. 4 and 5;

FIG. 7 a schematic perspective view of a fin compression mold of the finproduction machine shown in FIG. 6; and

FIG. 8 a schematic view of pipe conduit expansion tools of a pipeconduit expansion machine.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a power plant 1 in one embodiment of the present invention.The power plant 1 in the present case is a gas turbine power plant,which may in principle likewise be any type of power plant. The powerplant 1 comprises an air compressor 2, a gas turbine 3, a generator 4and a transformer 5. During the operation of the power plant 1, aircompressed by the air compressor 2 is mixed with fuel in a known manner,and the air-fuel mixture is ignited. The resultant combustion gas issupplied to the gas turbine 3, where it is expanded to drive a gasturbine rotor 6. The gas turbine rotor 6 drives the rotor 46 of thegenerator 4, which converts the kinetic energy to electrical energy. Thetransformer 5 transforms the electrical energy in such a way that it canbe fed to a power supply grid. The generator 4 is supplied by DC powerin operation via contact rings or a brushless exciter 47.

The generator 4 is cooled using generator cooling gas, which iscirculated through a generator cooling circuit 7 by means that are notshown in detail. The generator cooling gas is recooled by provision of aheat exchanger 8 in one embodiment of the present invention. In the heatexchanger 8, the generator cooling gas is cooled firstly using coolingwater that circulates in a cooling water circuit 9, and secondly bymeans of a coolant that circulates in a coolant circuit 10. The coolingwater circuit 9 in the present case is what is called the intermediatecooling water circuit of the power plant 1, to which further heatexchangers are also connected, by means of which lubricant oil, sealingoil, pumps and/or other components of the power plant 1, for example,are cooled. The coolant circuit 10 through which the coolant flowscomprises a cooling unit for recooling of the coolant. The coolant usedin the present context is tetrafluoroethane (R-134a). Alternatively, itis also possible to use another coolant such as carbon dioxide, to givejust one example.

During the operation of the power plant 1, the generator cooling gasremoves heat from the generator 4, is recooled in the heat exchanger 8and then is guided back into the generator 4. In the heat exchanger 8,the heat withdrawn from the generator cooling gas is transferred firstlyto the cooling water that flows through the cooling water circuit 9 andsecondly to the coolant that flows through the coolant circuit 10.

A significant advantage of the power plant 1 shown in FIG. 1 is that thegenerator cooling gas that flows through the generator cooling gascircuit 7 is recooled not solely by means of cooling water butadditionally by means of a coolant. In this way, the cold gastemperature of the generator cooling gas on entry into the generator 4is adjustable or controllable very flexibly and as required. A furtheradvantage is that the generator cooling gas is recooled by the coolingwater and by the coolant in a single heat exchanger 8, since the use ofa single heat exchanger 8 saves construction space. This is ofparticular importance especially when an existing heat exchanger of apower plant in which the recooling is effected solely using coolingwater is to be replaced by a heat exchanger of the invention, since theconstruction space that is then available is defined by the dimensionsof the old heat exchanger and is correspondingly limited.

FIG. 2 shows one possible design of a heat exchanger 8 of the invention.The heat exchanger 8 through which a generator cooling gas flows in aflow direction indicated by the arrows 11 comprises a first stack offins 12 having a multitude of first fins 14 stacked in a stackingdirection that extends transverse to the flow direction indicated by thearrow 13. The first fins 14, as shown in FIG. 4, are each provided witha multitude of first passage holes 15 that are flush with one another instacking direction. The heat exchanger 8 further comprises at least onefurther stack of fins 16 arranged adjacent to the first stack of fins 12in flow direction and having a multitude of second fins 17 stacked inthe stacking direction, wherein the second fins 17 are each providedwith a multitude of second passage holes 18 that are flush with oneanother in stacking direction.

The first fins 14 and the second fins 17 are each produced from sheetmaterial, in the present case from aluminum, wherein the first fins 14and/or the second fins 17 may be provided with a coating on one or bothsides. The first fins 14 differ from the second fins 17 firstly in thatthey have a greater area. Secondly, the surfaces of the first fins 14,apart from the first passage holes 15, in the present case are smooth,whereas the surfaces of the second fins 17 are structured. Thestructuring in the working example presented is defined by elevatedregions 19 that are slotted at the side and are provided in the upwarddirection, which increases the surface areas of the second fins 17 andinfluences the flow of the generator cooling gas through the furtherstack of fins 16. However, it should be pointed out that the design ofthe surfaces both of the first fins 14 and of the second fins 17 may inprinciple vary as required. A further difference is that a distance a₁between the first fins 14 in stacking direction is greater than adistance a₂ between the second fins 17 in stacking direction.Furthermore, the arrangement patterns of the first passage holes 15differ from the arrangement patterns of the second passage holes 18, asapparent from FIGS. 3 and 4.

The heat exchanger 8 further comprises first pipe conduits 20 thatextend through the first passage holes 15 of the first fins 14 of thefirst stack of fins 12 and are press-fitted with the first fins 14, andsecond passage holes 21 that extend through the second passage holes 18of the second fins of the at least one further stack of fins 16 and arepress-fitted with the second fins 17. The first pipe conduits are eachconnected to one another via U-shaped connecting conduits 22, and thecooling water flows through them successively, entering the first stackof fins 12 in the direction of the arrow 23 and exiting therefrom in thedirection of the arrow 24. The second pipe conduits 21 are eachconnected to one another by U-shaped connecting conduits 25, and thecoolant flows through them successively, entering the further stack offins 16 in the direction of the arrow 26 and exiting therefrom in thedirection of the arrow 27. The first pipe conduits 20 and the secondpipe conduits 21 have each been produced from a metallic material, fromcopper in the present case, where the flow cross section of the firstpipe conduits 20 is greater than the flow cross section of the secondpipe conduits 21. The inner faces of the first pipe conduits 20 and/orthe inner faces of the second pipe conduits 21 may be structured inorder to increase their surface area.

The heat exchanger 8 additionally comprises an upper cover and lowercover 28, each of which connect the first stack of fins 12 and thefurther stack of fins 16 to one another. The covers 28 are respectivelyplaced onto the outer first fins 14 of the first stack of fins 12 andonto the adjacent outer second fins 17 of the further stack of fins 16in stacking direction from the bottom and from the top, and cover thesefins 14 and 17. The covers 28 have been provided with first passageopenings 29 that are arranged and formed so as to correspond to thefirst passage holes 15 of the first fins 14 of the first stack of fins12, through which the first pipe conduits 20 are conducted, and withsecond passage openings 30 that are arranged and formed so as tocorrespond to the second passage holes 18 of the second fins 17 of thefurther stack of fins 16, through which the second pipe conduits 21 areconducted. The covers 28 have been produced from a metallic material, inthe present case each from a metal sheet of aluminum. They firstly havechamfers 31 that point in the direction of the stacks of fins 12 and 16,which encompass these opposite sides, and secondly chamfers 32 thatpoint outward, which serve to protect the pipe conduits 20, 21 or theconnecting conduits 22, 25 that connect these to one another. The covers28 are connected to one another via struts 33 in the present case, whichimpart good mechanical stiffness to the heat exchanger.

FIG. 6 shows a schematic of a fin production machine 34 with a sheetmetal roll accommodation device 36 that accommodates a roll of sheetmetal 35, a sheet metal conveying device 37, a fin pressing device 38having an upper fin press mold 39 and a lower fin press mold 40, a fintransport device 41 and a fin stacking device 42.

During the operation of the fin production machine 34, sheet metal fromwhich the first fins 14 and the second fins 17 are to be manufactured isunwound by means of the sheet metal conveying device 37 from the roll ofsheet metal 35 that is held by the sheet metal roll accommodation device36 and fed to the fin pressing device 38. Both the first fins 14 and thesecond fins 17 are formed therein by movement of the fin press molds 39and 40 together and movement thereof away from one another. As shown inFIG. 7, the fin press molds 39 and 40 have different regions A1, A2, A3,A4, B1, B2, B3 and B4, which form features of the fins 14 and 17. Theregions identified by A form features of the first fin 14, and theregions identified by B form features of the second fin 17. The regionsidentified by number 1 form slots in the sheet metal; the regionsidentified by number 2 expand slotted regions; the regions identified bynumber 3 perform deep drawing of the sheet metal. The first fins 14 andsecond fins 17 manufactured in this way in the fin pressing device 38are then moved using the fin transport device 41 to the fin stackingdevice 42, where the first fins 14 and the second fins 17 arerespectively stacked one on top of another.

The stacked fins 14 and 17 are then moved to a pipe conduit expansionmachine 43. The pipe conduits 20 and 21 that have been introduced in themeantime into the corresponding passage holes 15, 18 of the stacked fins14, 17 are expanded simultaneously therein using suitably shaped pipeconduit expansion tools 44 by pushing the pipe conduit expansion tools44 through the pipe conduits 20, 21 from the top in the direction of thearrows 45.

In further steps, the covers 28, the struts 33 and the connectingconduits 22, 25 are mounted.

Even though the invention has been further illustrated and described indetail by the working example, the invention is not limited by theexamples disclosed, and other variations may be derived therefrom by theperson skilled in the art without departing from the scope of protectionof the invention.

1. A heat exchanger, through which a medium to be cooled flows in a flowdirection during operation thereof, comprising: a first stack of finshaving a multitude of first fins stacked in a stacking direction thatextends transverse to the flow direction, wherein the first fins areeach provided with a multitude of first passage holes that are flushwith one another in stacking direction, at least one further stack offins arranged adjacent to the first stack of fins in flow direction, andhaving a multitude of second fins stacked in the stacking direction,wherein the second fins are each provided with a multitude of secondpassage holes that are flush with one another in stacking direction,first pipe conduits that extend through the first passage holes of thefirst fins of the first stack of fins and are press-fitted with thefirst fins, second pipe conduits that extend through the second passageholes of the second fins of the at least one further stack of fins andare press-fitted with the second fins, wherein the first pipe conduitsand the second pipe conduits are not connected to one another for flowpurposes and are provided for passage of a first cooling medium and asecond cooling medium, wherein the first and second cooling media aredifferent from one another, and at least one cover that connects thefirst stack of fins and the at least one further stack of fins to oneanother, which is placed atop an outer first fin of the first stack offins and atop the adjacent outer second fin of the at least one furtherstack of fins and covers these fins, wherein the at least one cover hasbeen provided with first passage holes arranged and formed so as tocorrespond to the first passage holes of the first fins of the firststack of fins, through which the first pipe conduits are guided, and hasbeen provided with second passage holes arranged and formed so as tocorrespond to the second passage holes of the second fins of the atleast one further stack of fins, through which the second pipe conduitsare guided.
 2. The heat exchanger as claimed in claim 1, wherein thefirst fins have a greater area than the second fins.
 3. The heatexchanger as claimed in claim 1, wherein the design of the surface ofthe first fins is different than the design of the surface of the secondfins.
 4. The heat exchanger as claimed in claim 1, wherein the firstfins and the second fins are produced from sheet material.
 5. The heatexchanger as claimed in claim 1, wherein a distance between the firstfins in stacking direction is different than the distance between thesecond fins in stacking direction, preferably greater.
 6. The heatexchanger as claimed in claim 1, wherein the first fins and the secondfins have been produced from a sheet material having a coating on one orboth sides.
 7. The heat exchanger as claimed in claim 1, wherein thefirst pipe conduits are each connected to one another via U-shapedconnecting conduits, and the first cooling medium flows through themsuccessively, and/or wherein the second pipe conduits are each connectedto one another by U-shaped connecting conduits, and the second coolingmedium flows through them successively.
 8. The heat exchanger as claimedin claim 1, wherein the flow cross section of the first pipe conduits isdifferent than the flow cross section of the second pipe conduits. 9.The heat exchanger as claimed in claim 1, wherein the first pipeconduits and the second pipe conduits have been manufactured from ametallic material.
 10. The heat exchanger as claimed in claim 1, whereinthe inner faces of the first pipe conduits and/or the inner faces of thesecond pipe conduits are structured.
 11. The heat exchanger as claimedin claim 1, wherein an arrangement pattern of the first passage holes isdifferent than the arrangement pattern of the second passage holes. 12.The heat exchanger as claimed in claim 1, wherein the at least one coverhas been produced from a metallic material, and/or from a metal sheet.13. The heat exchanger as claimed in claim 1, wherein the at least onecover encompasses the first stack of fins and the at least one furtherstack of fins on opposite sides.
 14. The heat exchanger as claimed inclaim 1, wherein the first stack of fins and the at least one furtherstack of fins are connected to one another by at least one strut.
 15. Aprocess for producing a heat exchanger as claimed in claim 1, whereinthe first fins and the second fins are produced simultaneously in asingle fin compression device.
 16. The process as claimed in claim 15,wherein the first pipe conduits and the second pipe conduits areexpanded simultaneously in a pipe conduit expansion machine.
 17. A powerplant comprising: a generator cooled by means of a generator coolinggas, and a heat exchanger as claimed in claim 1 that cools the generatorcooling gas.
 18. The power plant as claimed in claim 17, wherein thefirst cooling medium that flows through the heat exchanger is coolingwater and the second cooling medium that flows through the heatexchanger is a coolant.
 19. The heat exchanger as claimed in claim 5,wherein the distance between the first fins in stacking direction isgreater than the distance between the second fins in stacking direction.20. The heat exchanger as claimed in claim 8, wherein the flow crosssection of the first pipe conduits is greater than the flow crosssection of the second pipe conduits.
 21. The heat exchanger as claimedin claim 9, wherein the metallic material comprises copper.